Integer Constants


Integer constants are numbers that are used directly in a sketch, like 123. By default, these numbers are treated as int but you can change this with the U and L modifiers (see below).

Normally, integer constants are treated as base 10 (decimal) integers, but special notation (formatters) may be used to enter numbers in other bases.

Base Example Formatter Comment
10 (decimal)123none
2 (binary)B1111011leading 'B'only works with 8 bit values (0 to 255) characters 0&1 valid
8 (octal)0173leading "0"characters 0-7 valid
16 (hexadecimal)0x7Bleading "0x"characters 0-9, A-F, a-f valid

Decimal (base 10)

This is the common-sense math with which you are acquainted. Constants without other prefixes are assumed to be in decimal format.

Example Code:

n = 101; // same as 101 decimal ((1 * 10^2) + (0 * 10^1) + 1)

Binary (base 2)

Only the characters 0 and 1 are valid.

Example Code:

n = B101; // same as 5 decimal ((1 * 2^2) + (0 * 2^1) + 1)

The binary formatter only works on bytes (8 bits) between 0 (B0) and 255 (B11111111). If it is convenient to input an int (16 bits) in binary form you can do it a two-step procedure such as:

myInt = (B11001100 * 256) + B10101010; // B11001100 is the high byte`

Octal (base 8)

Only the characters 0 through 7 are valid. Octal values are indicated by the prefix "0" (zero).

Example Code:

n = 0101; // same as 65 decimal ((1 * 8^2) + (0 * 8^1) + 1)

It is possible to generate a hard-to-find bug by (unintentionally) including a leading zero before a constant and having the compiler unintentionally interpret your constant as octal.

Hexadecimal (base 16)

Valid characters are 0 through 9 and letters A through F; A has the value 10, B is 11, up to F, which is 15. Hex values are indicated by the prefix "0x". Note that A-F may be upper (A-F) or lower case (a-f).

Example Code:

n = 0x101; // same as 257 decimal ((1 * 16^2) + (0 * 16^1) + 1)


U & L formatters:

By default, an integer constant is treated as an int with the attendant limitations in values. To specify an integer constant with another data type, follow it with:

  • A 'u' or 'U' to force the constant into an unsigned data format. Example: 33u
  • A 'l' or 'L' to force the constant into a long data format. Example: 100000L
  • A 'ul' or 'UL' to force the constant into an unsigned long constant. Example: 32767ul

See Also


Arduino UNO R3
Arduino Starter Kit
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